The present invention relates to controlling conditions within a chamber for converting pulverulent raw materials to a liquefied state as a discrete step in a melting process. The invention is generally applicable to processes that involve thermally converting a subdivided, essentially solid state feed material to an at least partially melted state. The invention is particularly applicable to initially liquefying a transient layer of the material supported by a stable layer of granular, thermally insulating, non-contaminating material, e.g., liquefying a layer of glass batch supported by a layer of material such as a granular batch constituent or glass batch.
U.S. Pat. No. 4,381,934 to Kunkle et al. teaches a method of converting particulate batch materials to a partially melted, liquefied state on a pulverulent support surface compatible with the batch material. As taught therein, the initial process of liquefying batch material is isolated from the remainder of the melting process and is carried out in a manner uniquely suited to the needs of the particular step, thereby permitting the liquefaction step to be carried out with considerable economies in energy consumption and equipment size and cost.
In a preferred embodiment of the Kunkle invention, a drum portion of the melting chamber is mounted for rotation so that batch fed into the chamber is held against chamber side walls by rotation of the drum to maintain a stable layer along the interior of the drum. Thermal energy is supplied to the drum interior so that the batch layer encircles the heat source. The liquefaction process is carried out by feeding batch into the drum through a stationary lid while rotating the drum and supplying heat to the drum interior to melt incoming batch material in a transient layer while an underlying layer of batch remains substantially stable and unmelted. As the material is liquefied, it flows downward toward an exit end of the rotating drum.
Central to the Kunkle method is the concept of employing a non-contaminating, thermally insulating layer of granular material (e.g., glass batch itself) as the support surface upon which liquefaction of glass batch takes place. A steady state condition may be maintained in the liquefaction chamber by distributing fresh batch onto a previously deposited batch surface at essentially the same rate at which the batch is melting, whereby a substantially stable batch layer will be maintained beneath a transient batch layer, and liquefaction is essentially confined to the transient layer. The partially melted batch of the transient layer runs off the surface while contacting substantially only a batch surface, thus avoiding contaminating contact with refractories. Because glass batch is a good heat insulator, providing the stable batch layer with sufficient thickness protects any underlying support structure from thermal deterioration.
During operation, the thickness of the lining fluctuates as portions melt away and are subsequently replenished. Some of these fluctuations may be merely momentary, but practical limitations on the ability to maintain perfectly steady state conditions sometimes results in the lining having significantly different thicknesses at different times. It is desirable to deposit incoming batch material onto a preselected portion of the lining, the location of which varies as the lining thickness changes. Therefore, the ability to adjust the batch feed orientation is desirable. One approach to this problem is disclosed in U.S. Pat. No. 4,529,428 (Groetzinger) in which a pivotable plate is used to deflect the incoming batch stream onto the appropriate portion of the lining. While this approach can be effective, it would be desirable to provide an arrangement that would be simpler in construction and would not entail sharp changes in the direction of the batch stream so as to minimize scattering of the batch and entrainment of finer particles in the combustion gas streams.
Batch feed chutes that direct batch toward side wall portions of rotating melters are shown in U.S. Pat. Nos. 2,006,947 and 2,007,755 (both Ferguson). In the former, the angle of the feed chute is shown with a tangential component. Neither provides adjustability to the location at which batch is deposited.